This invention relates to a venetian blind, more particularly to a reliable and durable angle-controlling device for a venetian blind.
Referring to FIG. 1, a conventional venetian blind 10 includes a horizontal support 11 with a U-shaped cross-section, a rotating shaft 12 journalled on the support 11, two rotating wheels 13 sleeved rigidly on the shaft 12, a driving unit 14 consisting of a worm and a worm gear, a superposed series of horizontal slats 15, a bottom rail 15A disposed below the slats 15, two sets of two tilting cords 16, a pair of pull cords 17, 18, and a rotatable rod 19 actuatable manually to rotate the shaft 12 via the driving unit 14. The pull cords 17, 18 extend through the vertically aligned openings of the slats 15 to fasten to the bottom rail 15A. After the pull cords 17, 18 have been manipulated to move the bottom rail 15A to a desired point, a quick lock means 1A is activated to position the bottom rail 15A relative to the support 11. As shown in FIG. 2, each of the rotating wheels 13 consists of two tubular elements 131 sleeved rigidly on the shaft 12. The tilting cords 16 are clamped tightly between the tubular elements 131 so that the rotation of the shaft 12 can cause the tilting cords 16 to move up and down. Referring to FIG. 3, an alternative conventional rotating wheel is provided in the form of a single tubular element 13' with a hole 131' formed therethrough. One end of each of the tilting cords 16' is secured in a hole 131' of the tubular element 13'. When the rotatable rod 19 is inadvertently rotated several revolutions, the tilting cords 16, 16' are wound on the rotating wheel 13, 13', thereby resulting in either the angle of the slats 15 being uncontrollable or the breakage of the tilting cords 16, 16'.